Swift: Instantiate a view controller for custom transition in the current navigation stack

Question

Introduction

I'm creating an app that has, in its rootViewController, a UITableView and a UIPanGestureRecognizer attached to a small UIView acting as a "handle" which enables a custom view controller transition for a UIViewController called "SlideOutViewController" to be panned from the right.

Issue

I have noticed two issues with my approach. But the actual custom transition works as expected.

When the SlideOutViewController is created it is not attached to the navigation stack I believe, therefore it has no associated navigationBar. And if I use the navigationController to push it on the stack, I loose the interactive transition.
Side note: I have not found a way to connect the handle to the SlideOutViewController that is interactively dragged out. So the translation of the handle is not consistent with the SlideOutViewControllers position.

Question

How can I add the SlideOutViewController to the navigation stack? So that the SlideOutViewController transitions with a navigationBar when I trigger the UIPanGestureRecognizer?

My code

In the rootViewController.

class RootViewController: UIViewController {

    ...

    let slideControllerHandle = UIView()
    var interactionController : UIPercentDrivenInteractiveTransition?

    override func viewDidLoad() {
        super.viewDidLoad()

        ... // Setting up the table view etc...

        setupPanGForSlideOutController()
    }

    private func setupPanGForSlideOutController() {
         slideControllerHandle.translatesAutoresizingMaskIntoConstraints = false
         slideControllerHandle.layer.borderColor = UIColor.black.cgColor
         slideControllerHandle.layer.borderWidth = 1
         slideControllerHandle.layer.cornerRadius = 30
         view.addSubview(slideControllerHandle)
         slideControllerHandle.frame = CGRect(x: view.frame.width - 12.5, y: view.frame.height / 2, width: 25, height: 60)
         let panGestureForCalendar = UIPanGestureRecognizer(target: self, action: #selector(handlePanGestureForSlideOutViewController(_:)))
         slideControllerHandle.addGestureRecognizer(panGestureForCalendar)
    }

    @objc private func handlePanGestureForSlideOutViewController(_ gesture: UIPanGestureRecognizer) {

         let xPosition = gesture.location(in: view).x
         let percent = 1 - (xPosition / view.frame.size.width)

         switch gesture.state {
         case .began:
             guard let slideOutController = storyboard?.instantiateViewController(withIdentifier: "CNSlideOutViewControllerID") as? SlideOutViewController else { fatalError("Sigh...") }
             interactionController = UIPercentDrivenInteractiveTransition()
        slideOutController.customTransitionDelegate.interactionController = interactionController
             self.present(slideOutController, animated: true)
         case .changed:
             slideControllerHandle.center = CGPoint(x: xPosition, y: slideControllerHandle.center.y)
             interactionController?.update(percent)
         case .ended, .cancelled:
             let velocity = gesture.velocity(in: view)
             interactionController?.completionSpeed = 0.999
             if percent > 0.5 || velocity.x < 10 {
                 UIView.animate(withDuration: 0.5, delay: 0, usingSpringWithDamping: 0.8, initialSpringVelocity: 0.5, options: .curveEaseInOut, animations: {
                     self.slideControllerHandle.center = CGPoint(x: self.view.frame.width, y: self.slideControllerHandle.center.y)
                 })
                 interactionController?.finish()
             } else {
                 UIView.animate(withDuration: 0.5, delay: 0, usingSpringWithDamping: 0.8, initialSpringVelocity: 0.5, options: .curveEaseInOut, animations: {
                     self.slideControllerHandle.center = CGPoint(x: -25, y: self.slideControllerHandle.center.y)
                 })
                 interactionController?.cancel()
             }
             interactionController = nil
         default:
             break
         }
    }

The SlideOutViewController

class SlideOutViewController: UIViewController {

    var interactionController : UIPercentDrivenInteractiveTransition?
    let customTransitionDelegate = TransitionDelegate()

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        modalPresentationStyle = .custom
        transitioningDelegate = customTransitionDelegate
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .red
        navigationItem.title = "Slide Controller"
        let addButton = UIBarButtonItem(barButtonSystemItem: .add, target: self, action: #selector(addNewData(_:)))
        navigationItem.setRightBarButton(addButton, animated: true)
    }

}

The custom transition code. Based on Rob's descriptive answer on this SO question

TransitionDelegate

class TransitioningDelegate: NSObject, UIViewControllerTransitioningDelegate {

    weak var interactionController : UIPercentDrivenInteractiveTransition?
    func animationController(forPresented presented: UIViewController, presenting: UIViewController, source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        return CNRightDragAnimationController(transitionType: .presenting)
    }

    func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        return CNRightDragAnimationController(transitionType: .dismissing)
    }

    func presentationController(forPresented presented: UIViewController, presenting: UIViewController?, source: UIViewController) -> UIPresentationController? {
        return PresentationController(presentedViewController: presented, presenting: presenting)
    }

    func interactionControllerForPresentation(using animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
        return interactionController
    }    

    func interactionControllerForDismissal(using animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
        return interactionController
    }
}

DragAnimatedTransitioning

class CNRightDragAnimationController: NSObject, UIViewControllerAnimatedTransitioning {

    enum TransitionType {
        case presenting
        case dismissing
    }

    let transitionType: TransitionType

    init(transitionType: TransitionType) {
        self.transitionType = transitionType
        super.init()
    }

    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        let inView   = transitionContext.containerView
        let toView   = transitionContext.view(forKey: .to)!
        let fromView = transitionContext.view(forKey: .from)!

        var frame = inView.bounds

        switch transitionType {
        case .presenting:
            frame.origin.x = frame.size.width
            toView.frame = frame

            inView.addSubview(toView)
            UIView.animate(withDuration: transitionDuration(using: transitionContext), animations: {
                toView.frame = inView.bounds
            }, completion: { finished in
                transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
            })
        case .dismissing:
            toView.frame = frame
            inView.insertSubview(toView, belowSubview: fromView)

            UIView.animate(withDuration: transitionDuration(using: transitionContext), animations: {
                frame.origin.x = frame.size.width
                fromView.frame = frame
            }, completion: { finished in
                transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
            })
        }
    }

    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return 0.5
    }
}

PresentationController

class PresentationController: UIPresentationController {

    override var shouldRemovePresentersView: Bool { return true }
}

Thanks for reading my question.

Rob · Accepted Answer

The animation code you’ve taken this from is for custom “present” (e.g. modal) transitions. But if you want a custom navigation as you push/pop when using a navigation controller, you specify a delegate for your UINavigationController and then return the appropriate transitioning delegate in navigationController(_:animationControllerFor:from:to:). And also implement navigationController(_:interactionControllerFor:) and return your interaction controller there.

E.g. I'd do something like:

class FirstViewController: UIViewController {

    let navigationDelegate = CustomNavigationDelegate()

    override func viewDidLoad() {
        super.viewDidLoad()

        navigationController?.delegate = navigationDelegate
        navigationDelegate.addPushInteractionController(to: view)
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        navigationDelegate.pushDestination = { [weak self] in
            self?.storyboard?.instantiateViewController(withIdentifier: "Second")
        }
    }
}

Where:

class CustomNavigationDelegate: NSObject, UINavigationControllerDelegate {

    var interactionController: UIPercentDrivenInteractiveTransition?
    var current: UIViewController?
    var pushDestination: (() -> UIViewController?)?

    func navigationController(_ navigationController: UINavigationController,
                              animationControllerFor operation: UINavigationController.Operation,
                              from fromVC: UIViewController,
                              to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        return CustomNavigationAnimator(transitionType: operation)
    }

    func navigationController(_ navigationController: UINavigationController,
                              interactionControllerFor animationController: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
        return interactionController
    }

    func navigationController(_ navigationController: UINavigationController, didShow viewController: UIViewController, animated: Bool) {
        current = viewController
    }
}

// MARK: - Push

extension CustomNavigationDelegate {
    func addPushInteractionController(to view: UIView) {
        let swipe = UIScreenEdgePanGestureRecognizer(target: self, action: #selector(handlePushGesture(_:)))
        swipe.edges = [.right]
        view.addGestureRecognizer(swipe)
    }

    @objc private func handlePushGesture(_ gesture: UIScreenEdgePanGestureRecognizer) {
        guard let pushDestination = pushDestination else { return }

        let position = gesture.translation(in: gesture.view)
        let percentComplete = min(-position.x / gesture.view!.bounds.width, 1.0)

        switch gesture.state {
        case .began:
            interactionController = UIPercentDrivenInteractiveTransition()
            guard let controller = pushDestination() else { fatalError("No push destination") }
            current?.navigationController?.pushViewController(controller, animated: true)

        case .changed:
            interactionController?.update(percentComplete)

        case .ended, .cancelled:
            let speed = gesture.velocity(in: gesture.view)
            if speed.x < 0 || (speed.x == 0 && percentComplete > 0.5) {
                interactionController?.finish()
            } else {
                interactionController?.cancel()
            }
            interactionController = nil

        default:
            break
        }
    }
}

// MARK: - Pop

extension CustomNavigationDelegate {
    func addPopInteractionController(to view: UIView) {
        let swipe = UIScreenEdgePanGestureRecognizer(target: self, action: #selector(handlePopGesture(_:)))
        swipe.edges = [.left]
        view.addGestureRecognizer(swipe)
    }

    @objc private func handlePopGesture(_ gesture: UIScreenEdgePanGestureRecognizer) {
        let position = gesture.translation(in: gesture.view)
        let percentComplete = min(position.x / gesture.view!.bounds.width, 1)

        switch gesture.state {
        case .began:
            interactionController = UIPercentDrivenInteractiveTransition()
            current?.navigationController?.popViewController(animated: true)

        case .changed:
            interactionController?.update(percentComplete)

        case .ended, .cancelled:
            let speed = gesture.velocity(in: gesture.view)
            if speed.x > 0 || (speed.x == 0 && percentComplete > 0.5) {
                interactionController?.finish()
            } else {
                interactionController?.cancel()
            }
            interactionController = nil


        default:
            break
        }
    }
}

And

class CustomNavigationAnimator: NSObject, UIViewControllerAnimatedTransitioning {

    let transitionType: UINavigationController.Operation

    init(transitionType: UINavigationController.Operation) {
        self.transitionType = transitionType
        super.init()
    }

    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        let inView   = transitionContext.containerView
        let toView   = transitionContext.view(forKey: .to)!
        let fromView = transitionContext.view(forKey: .from)!

        var frame = inView.bounds

        switch transitionType {
        case .push:
            frame.origin.x = frame.size.width
            toView.frame = frame

            inView.addSubview(toView)
            UIView.animate(withDuration: transitionDuration(using: transitionContext), animations: {
                toView.frame = inView.bounds
            }, completion: { finished in
                transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
            })

        case .pop:
            toView.frame = frame
            inView.insertSubview(toView, belowSubview: fromView)

            UIView.animate(withDuration: transitionDuration(using: transitionContext), animations: {
                frame.origin.x = frame.size.width
                fromView.frame = frame
            }, completion: { finished in
                transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
            })

        case .none:
            break
        }
    }

    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return 0.5
    }
}

Then, if the second view controller wanted to have the custom interactive pop plus the ability to swipe to the third view controller:

class SecondViewController: UIViewController {

    var navigationDelegate: CustomNavigationDelegate { return navigationController!.delegate as! CustomNavigationDelegate }

    override func viewDidLoad() {
        super.viewDidLoad()

        navigationDelegate.addPushInteractionController(to: view)
        navigationDelegate.addPopInteractionController(to: view)
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        navigationDelegate.pushDestination = { [weak self] in
            self?.storyboard?.instantiateViewController(withIdentifier: "Third")
        }
    }

}

But if the last view controller can't push to anything, but only pop:

class ThirdViewController: UIViewController {

    var navigationDelegate: CustomNavigationDelegate { return navigationController!.delegate as! CustomNavigationDelegate }

    override func viewDidLoad() {
        super.viewDidLoad()

        navigationDelegate.addPopInteractionController(to: view)
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        navigationDelegate.pushDestination = nil
    }

}

Swift: Instantiate a view controller for custom transition in the current navigation stack

Introduction

Issue

Question

My code

Answers (1)

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